Dalecarlia Water Treatment Plant

Project Overview

Dalecarlia Water Treatment Plant, operated by the Washington Aqueduct, provides potable water supply to the District of Columbia, Arlington County and the City of Falls Church, VA. Removal of solid particles from the river intake (such as silts) occurs during the water treatment process, and historically these particles (or residuals) have been returned to the Potomac River. However, to meet updated 2004 EPA restrictions regarding the discharge of these residuals back to the river, the new Residuals Collection and Treatment Facility, Dalecarlia Water Treatment Plant, was designed and constructed to collect liquid residuals to a central processing location, allow residuals to thicken in large gravity tanks, then piped to the processing building for dewatering and loading onto trucks for offsite disposal.

Exterior appearance and noise mitigation were critical components of the facility, given its location adjacent to Sibley Hospital and local neighborhoods on both DC and Maryland sides of the site. The Residuals Collection and Treatment building exterior consists of brick veneer with four intermittent cast stone feature bands. Window and door surrounds are constructed with three corbelled header courses, which give depth and distinction to the openings. The four connecting gravity thickener tanks, each over 100 feet in diameter and up to 20 feet in height, also have two cast stone feature bands and brick to match with the Residuals building. In all, over 333,000 brick and 1,800 cast stone pieces were installed for the building and thickeners. The North and South elevations of the upper building (as well as the four gravity thickeners) utilize radius wall construction to further add to the architectural distinction of the building.

To address noise mitigation, all exterior backup walls for the building were constructed of 12-inch thick concrete masonry units(CMU), grouted, and all interior walls were constructed with a minimum of 8-inch thick CMU. At the 3rd floor centrifuge equipment level, 4-inch acoustical CMU units were installed against the 12-inch exterior CMU wall for additional noise reduction to the outside. Over 23,500 CMU pieces were installed in the Residuals Collection and Treatment facility.

Also assisting in the appearance and noise mitigation was the selection and grading of the site, for which much of the building and thickeners sit below the elevation of the street separating the site from Sibley Hospital and adjacent neighborhoods, basically sitting the project in a bowl. However, this also created significant problems in keeping the site dry for equipment access, which experienced periods of record precipitation during construction; all-terrain forklifts and crane equipment were quite often partially submerged in mud while servicing the masonry crews. Another obstacle we had to overcome on this project was the design of the building itself with the ground floor level being larger than the upper levels and creating a promenade deck with the main upper building being set back. This forced us to set our FRACO scaffold units on the second floor deck (with post shores down to the basement levels in some cases), and created problems with servicing the scaffold. We ultimately ended up using both a boom truck and hydro cranes to stock materials and equipment once we were out of reach for our forklifts.

In the end, the Washington Aqueduct was pleased with the exterior façade they have provided to the public, and Calvert Masonry is pleased to have been part of this design and construction team.